1. Field of Application
The present invention relates to a vehicle control apparatus for use in a control system of a vehicle in which a plurality of vehicle control apparatuses have respective communication apparatuses for mutual communication. In particular, the invention relates to a vehicle control apparatus used in a vehicle in which two or more of the vehicle control apparatuses become activated at respectively different time points, e.g., by a system such as a wake-up system.
2. Description of Related Art
Present-day motor vehicles are equipped with various control apparatuses for controlling equipment of the vehicle, such as an engine ECM (engine control module), alternator ECU 2 (electronic control unit), transmission ECU, etc., with data communication being performed between the various control apparatuses. The respective time points at which these control apparatuses become activated (specifically, become capable of beginning communication, after power commences to be supplied to the control apparatus) are not necessarily identical. For example the case will be considered in which a vehicle control apparatus A receives data transmitted from a vehicle control apparatus B, but the activation time point of the vehicle control apparatus A is prior to that of the vehicle control apparatus B. It will further be assumed that the vehicle control apparatus A has a buffer having a region that is reserved for holding data received from the vehicle control apparatus B, with that data being used in processing executed by vehicle control apparatus A.
In such a case, there will be a delay interval during which the vehicle control apparatus A is activated but the vehicle control apparatus B is not yet activated. This can result in the following problems. The contents of the aforementioned buffer of the vehicle control apparatus A, during the activation delay interval, will in general not constitute data that have been recently received from the vehicle control apparatus B. Hence use of the buffer contents in processing that is executed by vehicle control apparatus A may result in faulty operation by the vehicle control apparatus A, so that appropriate control cannot be achieved.
A further problem that may result from the activation delay interval is that the vehicle control apparatus A may judge that the amount of data stored in the buffer (specifically, a region used to hold data received from the vehicle control apparatus B) is incorrect, and may thereby wrongly judge that a failure condition has occurred (i.e., a failure condition of the vehicle control apparatus B, or a failure in communication with the vehicle control apparatus B), whereas the problem is caused only by the delay in activating the vehicle control apparatus B.
This problem is especially liable to occur in the case of a vehicle using a wake-up system for activating various vehicle control apparatuses, so that some vehicle control apparatuses are activated prior to switch-on of the vehicle main power source (i.e., ignition switch-on) and other vehicle control apparatuses become activated after that switch-on has occurred.